shallowCompare.js

function shallowCompare(a, b) {
  if (a === b) {
    return true;
  }
  if (typeof a === 'object' && typeof b === 'object' && hiddenClass(a) === hiddenClass(b)) {
    return !memcmp(a, b, sizeOfClass(a));
  }
  if (typeof a === 'function' && typeof b === 'function') {
    if (sourceLocation(a) === sourceLocation(b)) {
      return shallowCompare(getClosureContextOf(a), getClosureContextOf(b));
    }
  }
  return false;
}

function memoize(fn) {
  var lastArg, lastResult;
  return function(arg) {
    if (lastArg && shallowCompare(lastArg, arg)) {
      return lastResult;
    }
    lastArg = arg;
    lastResult = fn(arg);
    return lastResult;
  };
}

var memoizedRender = memoize(render);

var obj = {};
memoizedRender({ a: 123, b: obj });
memoizedRender({ a: 123, b: obj }); // fast path

var captured = 123;
function renderWithCallback() {
  return memoizedRender(function foo() {
    return captured;
  });
}

renderWithCallback();
renderWithCallback(); // fast path because the result is memoized